The invention relates to a wheel hub for receiving a brake disk, particularly a wheel hub for commercial vehicles, having a hub body which is molded to the wheel flange and has a neck section designed for receiving the brake disk.
Wheel hubs of this type are used on powered axles and dead axles of road vehicles, particularly of commercial vehicles, having disk brakes.
Such wheel hubs have the problem of thermal stress to the wheel bearings and the lubricant as a result of a heat development in the wheel bearing as well as, under certain circumstances, also because of the heat transmission from the brake disk to the hub body.
In the case of a high loading of the vehicle, considerable heat is necessarily developed in the wheel bearing because of the resulting friction in the bearing. The heat development may be increased by the heating-up of the brake disk during brakings. Since, for the purpose of the braking torque transmission, the brake disk is mechanically (in one part or in several parts) connected with the wheel hub, a portion of the heat generated in the brake disk is transmitted to the wheel hub. The heat development in the wheel bearing, like the heat development in the brake disk, is approximately proportional to the loading condition of the vehicle or the loading of the respective wheel. In the case of a high loading of the vehicle—connected with a braking-intensive driving method, for example, during drives in mountainous regions—the occurring thermal stressing of the wheel hub may be relatively high.
According to the type of construction of the brake disk and the type of hub linkage, different conditions exist for the thermal stressing and cooling of the wheel hub.
FIGS. 8 to 11 show different wheel hub/brake disk combinations.
FIG. 8 shows a wheel hub/brake disk combination in which, for the purpose of a fastening to the wheel hub, the brake disk is provided with a neck and a flange and, by way of this flange, is connected with the wheel hub by means of the wheel bolts which are also used for fastening the vehicle wheel to the wheel hub. In this type of construction, only a low heat transmission takes place by a direct heat conduction from the brake disk to the wheel hub bearing area because the fastening and the resulting heat-conducting contact of the brake disk onto wheel hub takes place at the outer circumference of the latter.
In contrast, the enveloping of the hub body by the brake disk neck is less optimal, which enveloping, on the one hand, results in a thermal radiation from the brake disk neck to the surface of the hub body and, on the other hand, hinders the dissipating of the frictional heat occurring in the wheel bearing to the environment.
FIG. 9 shows a similar hub/brake disk combination in which the brake disk is fastened on the wheel hub by means of a separate screw flange. The heat transmission and heat dissipation conditions correspond essentially to FIG. 8.
FIG. 10 shows another two-part wheel hub/brake disk combination, in which the wheel hub is divided into a hub part (neck section) accommodating the wheel bearing and into the wheel flange carrying the vehicle wheel, and the brake disk equipped with a neck and an inward-pulled ring flange is clamped in between the hub part and the wheel flange by a screwing-together of these two parts. In the case of this type of construction, in addition to the limited heat dissipation by way of the surface area of the hub because of the enveloping by the brake disk neck, there is the problem that the hub part is separated from the wheel flange by the brake disk clamped in-between, and the heat dissipation capacity of the wheel flange is therefore not utilized for the hub.
FIG. 11 shows a wheel hub/brake disk combination of the initially mentioned type in which an internally ventilated brake disk with two friction rings, by way of a non-circular profile, for example, a toothing, generated on the inside diameter, engages in an essentially oppositely designed contour on the circumference of the wheel hub. The heat-conducting contact of the brake disk with respect to the wheel hub is preferably interrupted by heat-insulating intermediate elements in order to thus reduce the thermal stressing of the wheel hub. In this case, the brake disk may be detachably connected with the hub body or may be joined onto the wheel hub in an undetachable manner, for example, by means of a composite casting method. Since, as a result of the heat-insulating intermediate elements, only a slight heat dissipation takes place from the brake disk by way of the wheel hub, such brake disks have slightly higher operating temperatures than the above-described neck-type and cup-type brake disks. On the other hand, the enveloping of the hub body by the (non-existing) brake disk neck does not take place, whereby the heat dissipation from the wheel hub is improved.
In contrast to this heat-dissipating construction, which is satisfactory per se, it is an object of the invention to further develop the wheel hub such that the releasing of heat to the environment is improved, particularly during braking.
According to the invention, the neck section is provided with a surface structure which increases the heat discharge to the environment—preferably relative to a uniform or tapering or widening cylinder surface—in the axial area adjoining the area for the placing of the brake disk. As a result of this simple and cost-effective measure, the heat discharge of the wheel hub to the ambient air can be effectively increased. The invention is particularly suitable for a two-part embodiment of the wheel hub and the brake disk, in which case the brake disk is placed upon the wheel hub. Summarizing, the invention implements a wheel hub for a wheel hub/brake disk combination with, in one embodiment, a flat, tooth-linked brake disk, in the case of which the exposed wheel hub surface is utilized in the sense of an improved heat dissipation from the wheel hub and the brake disk. In this manner, a thermal overloading of the wheel hub is effectively avoided.
In the axial area adjoining the area for the placing of the brake disk, the neck section is preferably provided with ribs. With respect to their manufacturing, these “cooling ribs” and be implemented in a simple manner in the case of a cast hub and provide a good heat dissipation. For a further improvement of the cooling of the wheel hub, ducts are preferably constructed between the axially extending ribs, in which ducts an air flow is formed during the rotating of the wheel hub on the axle. The ribs and the ducts preferably extend to a wheel flange molded to the neck section.
The ribs preferably extend on the outer circumference of the neck section essentially in the axial direction, so that the ventilating effect is optimized. It is also conceivable to mutually connect the axial ribs by additional ribs extending in the circumferential direction in order to increase the rigidity of the wheel hub in a simple manner and thereby further simplify the use of light metals. The ribs extending in the circumferential direction, if required, may in turn have openings penetrating them for improving the air supply.
As a result of the forced ventilation of the hub body with cool fresh air from the exterior side of the vehicle wheel, an intensive heat dissipation is achieved from the wheel hub as well as additionally a cooling of the brake disk. As a result, not only the effects of the heat transmission from the brake disk to the wheel hub can be compensated, but the frictional heat forming in the wheel bearing can also be efficiently dissipated from the wheel hub and thus heats up the wheel bearing less intensively. As a result of the cooling of the wheel hub, even the use of light-weight materials as the wheel hub material becomes conceivable. In particular, it is also permitted by means of the invention to use a light-weight material, such as a light metal, for producing the wheel hub because the wheel hub is heated up less intensively. As a result of the selected rib structure, the hub body is reinforced which, in a supplementary manner, simplifies the use of light-weight materials. However, it is also conceivable for the wheel hub to consist of cast iron or steel.
Particularly preferably, at least some of the ducts lead into openings in the wheel flange, which penetrate the wheel flange. In this fashion, the air passage openings increase the air flow at the wheel hub in a simple manner and “suction” the ambient air through the ducts during the rotation of the wheel hub.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.